Damn Interesting

Express Elevator to Space, Going Up

Only a handful of decades ago, a group of very smart scientists figured that if they crammed a giant metal barrel full of explosive chemicals and bolted on a little compartment for people or cargo, they could light the fuse and use the resulting explosion to propel the stuff into outer space. They called this assembly a “space rocket,” and aside from a few dozen catastrophic failures, the idea has been working swimmingly ever since. Unfortunately, moving stuff into space with rockets isn’t particularly economical, costing about $10,000 per pound even when the assembly doesn’t blow up. A single launch of the reusable US space shuttle costs roughly $500 million in total.

The problem is that the Earth’s escape velocity (the speed required to escape Earth’s gravity) is so bloody high. A rocket, which often weighs tens of thousands of pounds, must push that enormous weight up to about 25,200 miles per hour, and sustain such speeds for several minutes. The rocket must carry so much fuel to sustain these speeds that the fuel makes up a significant portion of the vehicle’s weight, meaning that much of the fuel is spent lifting the rest of the fuel off the ground.

Because there has been no alternative (aside from avoiding outer space altogether), humankind has been stuck with this method of Earth egress for as long as such efforts have been undertaken. Many clever people have contemplated the idea of a tower or cable that can reach into Earth’s orbit and ferry people and cargo into space and back with much less energy, but when knowledgeable persons took to scribbling out the calculations, they found that the tower was physically impossible, and that the strongest material known to man was only half the strength necessary to make a cable reaching into space. But all of that changed in 1991, when carbon nanotubes came along and offered a possible solution.

Carbon nanotubes are made from the same carbon atoms that make up diamonds, but arranged in long, hollow, tube-like molecules. The molecular bonds in these molecules give the structures incredible tensile strength, and some degree of flexibility. A single molecule, though 50,000 times thinner than a human hair, can be theoretically made into a nanotube of any length. A number of these nanotubes can then be compressed into an extremely sturdy wire; enough to withstand the pressure needed for a space elevator.

The space elevator concept is relatively straightforward… it consists of a long carbon nanotube cable with one end attached to a fixed point on the Earth (or on an ocean-going platform), and the other end extending well beyond geosynchronous orbit. The centrifugal force caused by the Earth’s rotation would keep the cable taut, and thereby maintain the elevator’s fixed position. Large, tram-like elevator cars would then use electric motors to move themselves up the cable, and be accelerated as the Earth’s centrifugal force begins to propel them. After dropping off their payload in orbit, they could slowly descend in a similar fashion.

Despite the straightforward concept, construction of the elevator will be an engineering feat if it ever comes to fruition. It will require technologies that do not exist today, and some creative problem solving. For instance, as of this writing, the longest nanotubes to be developed are measured in centimeters, and a space elevator cable would need to be about 62,000 miles long. But researches all over the globe are addressing the problems, and despite the hurdles, optimistic estimates put a working space elevator in action as early as 2018. Although the project would cost several billions of dollars, it would reduce the stuff-to-orbit cost from $10,000/pound to less than $400/pound, so it should pay for itself in about a decade.

Researchers also need to anticipate and plan for what might go wrong with a space elevator. The airspace surrounding the elevator would need to be kept entirely clear of aircraft, lest a collision destroy the aircraft and compromise the integrity of the elevator. Satellites would also pose a hazard, since on a long enough timeline, all non-synchronous satellites will eventually reach a collision state with the elevator unless they are redirected. There are also natural factors, such as meteoroids and micrometeorites; ice formation on the cable; lightning and wind.

If the space elevator were to break near the Earth, the elevator would become unstable, and raise to a higher orbit. If it were to break nearer the top, the top section would raise to a higher orbit, and what cabling didn’t burn up in re-entry would theoretically drift to the Earth with all the force of a falling sheet of paper, given the cable’s light weight and flat, ribbon-like design. Any elevator cars would require an emergency descent system in the event of an emergency, perhaps using a system of parachutes.

NASA is currently exploring the possibility of a space elevator, and has identified several areas of critical research before one might be made feasible and practical. A space elevator has long been the stuff of science fiction, but with the discovery and development of carbon nanotubes, it may just be the primary vehicle to space in the coming decades.

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Kim Stanley Robinson’s novel Red Mars uses space elevators extensively, and gives a very realistic account of a possible way to construct, use, and the possible outcome of a failure of such a device.

Alan Bellows

Posted 31 October 2005 at 03:22 pm

Marius said: “Kim Stanley Robinson’s novel Red Mars uses space elevators extensively, and gives a very realistic account of a possible way to construct, use, and the possible outcome of a failure of such a device.”

So what sort of failure state did the books describe? I have heard theories where a space elevator falls to the earth at great speeds, wreaking meteoric destruction as it goes, but any material with the weight to do that is theoretically too heavy to use for a space elevator.

Bryan Lowder

Posted 31 October 2005 at 04:29 pm

I haven’t read Red Mars, but another excellent book is _Fountains_of_the_Gods_ by Arthur C. Clarke. The book is excellent in technical detail. In this book, he claims diamond tape would do the trick. Also, one failure mode is similar to the Tacoma Narrows bridge disaster– being essentially a long string, some source of energy that hit the right resonance mode would cause vibrations that would build to dangerous amplitudes. As I recall, the vibrations were actually caused by the car going up the cable. The solution was a large counterweight at the orbital end to change the resonant frequency. In the book, Mars was the first to get an elevator, because of the reduced strength requirement. Deimos became a counterweight. To avoid Phobos, the cars were timed to cause the cable to *twang* to one side at just the right moment. Not an engineering solution I would embrace.

The best discussion of this concept I have read is in Robert L. Forward’s book _Future_Magic_. Forward also discusses some really great interim concepts. One, the Launch Loop, could be executed today. Another, the Rotovator, is a stopgap solution between rockets and elevators.

In the Launch Loop, steel bars are accelerated by electromagnetic cannons and tossed into a great arc. On the other end, the bars are caught and re-accelerated. The bars interact magnetically with a pipe structure that encloses them all, and is empty of air. The loop hangs in the air without being strong enough to hold itself up. Coupling a car somehow into the stream would permit one to race to the top and fly off into orbit.

In the Rotavator, a three-spoked wheel with long cables for spokes orbits the Earth. At the same time, it is rotating as though it were “rolling” on the ground. The ends of the cables then execute a motion that essentially dives straight out of the sky. While it hangs there for a few minutes, a high-altitude airplane hooks you up to the end. Then you are jerked up into the sky. At the other end, you are flung off at twice orbital velocity– going anywhere you like. A Kevlar rotovator would be strong enough to operate on the Moon.

Alan Bellows said: “So what sort of failure state did the books describe? I have heard theories where a space elevator falls to the earth at great speeds, wreaking meteoric destruction as it goes, but any material with the weight to do that is theoretically too heavy to use for a space elevator.”

In the book the elevator in question is on Mars, and it is destroyed in a terrorist attack. The upper parts of the cable do burn up even in the thin Martian air, but the lower several miles wreak great havoc on impact. The weight of the cable itself seemed not insubstantial, but it has been several years since I read it, and some of the details are a bit fuzzy.

Josh Harding

Posted 01 November 2005 at 12:27 pm

Why don’t we just stick with transporters….they are safer right?

Bryan Lowder

Posted 01 November 2005 at 05:59 pm

Aw, shucks, Alan.

Seriously, I love this topic. I was a little jealous that you got to it first, but I hope you forgive me for being a
know-it-all. Don’t mean to steal your thunder, Alan. You’re _my_ hero, as you have produced roughly 25
articles for each one I write.

Another idea I think is just dandy– Infrared laser pointing straight up, put a Volkswagon-sized cargo with
reflective nozzle in the beam, water dribbles out the spigot, and the vessel shoots into the heavens on a pillar
of water plasma. Newer designs just use heated air. It’s another one of those ideas that are like rockets, but
that separate the reaction mass from the energy driving it. Other examples include solar sails, laser sails,
nuclear rockets (such as the “flying crowbar”) and mass drivers (essentially magnetic rail guns shooting out
boxes of rocks).

Josh Harding said: “Why don’t we just stick with transporters….they are safer right?”

If I understand the latest theoreticians, a “transporter” would get around the Heisenberg uncertainty effect
by annihilating atoms, producing two particles. One would transmit “quantum information” that could travel
faster than light, but that would be destroyed if observed. The other particle would transmit ordinary
info at light speed. They could recombine in a new location, reconstructing the exact quantum state of the
original atom.

The other form of teleportation (I came up with this one) would require advanced molecular nanotechnology.
A person would be chemically cross-linked to keep every molecule in its place (formaldehyde does this, to a
degree, and so does freezing). The person would then be fed into a nano-disassembler, which would take the
person apart molecule-by-molecule in a destructive fashion. The information about each atom’s position
would be encoded and beamed to a corresponding assembler, which would make a new you layer by layer
from raw materials. Once the cross-linking was reversed, you would wake up elsewhere.

Sure transporters are safer, Josh. You first. You may feel a tingling sensation….

Alan Bellows

Posted 01 November 2005 at 06:34 pm

Brilliant! I must say that these ideas would make excellent topics for whole articles, rather than just brief mentions in the Comments section (hint hint, nudge nudge).

JustAnotherName

Posted 05 November 2005 at 07:21 am

Hi. I have an IQ of 131. Enuff sed. I just wanted to say the article and all your posts are very good. Of course, I don’t understand most of the theories but I am glad you do. Now, could someone please find an article about STRINGS; a topic well covered by NOVA but I would love to read an article about it and read your comments.

slappykincaid

Posted 21 January 2006 at 01:59 pm

Bryan Lowder said: If I understand the latest theoreticians, a “transporter” would get around the Heisenberg uncertainty effect by annihilating atoms, producing two particles. One would transmit “quantum information” that could travel faster than light, but that would be destroyed if observed. The other particle would transmit ordinary info at light speed. They could recombine in a new location, reconstructing the exact quantum state of the original. “

. You are correct about that. A good book for such a topic would be …. well I do not remember the name, but the title is one word, and it has (of course) Albert Einstein on the cover. Well anyway, that (the above quote by Bryan Lowder)is an approximate summary of something I read on a physist’s homepage. That is the current theory, and I also enjoyed reading your theory. If someone finds the title of that book, post back to me, because I only read the synopsis, and I’d like to read the actual book.

naughtyhorse

Posted 16 October 2006 at 07:05 am

I have never read such tosh in all my life, actually I have read such tosh and it makes my blood boil every time I read it. forget nanotubes and patting yourself on the back in a self congratulatory manner (like good ol arthur has been doing for decades) and think like an 8th grade physics student (i.e. one with considerably more insight than the guy who thought this one up) cenrefugal (centrepetal) force will not hold up the cable under zero load and as soon as you load it what happens is the ‘car’ remains stationary and winds the cable back to earth (marginally faster than it would have be falling anyway). THINK about it. To escape the gravity well you need to do work to overcome the effect. In this scheme the work done is transferred to the cable, and transferred to the part of the cable above the car as tension, this tension transfers the load to….. what exactly? with a mass of what exactly. which, when the force on the cable acts on it will react HOW exactly?

Anyone want to buy a few hundred kilometers of mangled twisted buckminster fullerene tubes?
‘pulling oneself up by the bootsraps’ ony works in computer terms, in the real world you just look foolish
And to help you spot garbage like this in future remember “there is no such thing as a free lunch”

Whyaduck

Posted 17 October 2006 at 10:24 pm

Ummm…does anyone understand what naughtyhorse is trying to say? Here’s the deal…the elevator would be in geosynchronous orbit around the earth. It’s not held up by centripetal or centrifugal force. A car moving up the elevator is analogous to a train running across the landscape on the earth. And like a train running across the earth, it requires energy to go up and down the cable; the big difference is that it doesn’t have to carry it’s energy in a big honking tank and lift it along with its cargo. There are certainly big engineering challenges to be overcome, but the general concept is sound.

naughtyhorse

Posted 20 October 2006 at 06:07 am

whut???

do you actually know how a geosynchronous orbit works?
magic?
willpower?
pixie dust?
An object in geosynchronous orbit is held in place by cenrepetal force. it has mass, it has velocity, it is in earths gravitational field.
Newtons first law of motion states that

I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

i.e. the mass and velocity tend to make the object ‘want’ to head off into space along a straight line. Earth’s gravity modifies the path to maintain the orbit.
THATS HOW ORBITS WORK!
it’s (geosynchronous) a static system. It all has to balance. If it dont balance you dont have an orbit.
if one then attaches a rope to said object and applies a load to the rope (an elevator car ascends by effectively pulling down on the cable {no, it dosent matter where the winch engine is, on earth, in the car, or in space. no, nor the power supply either }) this load acts in the same direction as the force of gravity. that is to say ADDS to the force of gravity. at the risk of repeating myself the force acting down towards the earth gets BIGGER.

so, we have a geosync orbit, so we cant move or accelerate, cant increase the mass of the satellite, so the first clause of Newton 1 is still the same, but the modifying force (gravity plus the imposed load of the elevator car) is bigger.
balance is lost
as the force acting back down to earth is greater the orbit decays
when the orbit reaches the earths surface, the earths surface exerts a force on the satellite causing the satelite to come to rest (abruptly)
Consider the train “running across the earth” the mass of the train is attracted to the mass of the earth (gravity) and that force acts down. down throught the tracks and into the earth. irrespective of the state of motion of the train. obviously if the train is going up or down a grade then the force of gravity aids or hinders the work done by the engine (parallelogram of forces)
google ‘mass’ and ‘weight’ and consider the difference then you will see.
as i said
tosh

TomK

Posted 21 October 2006 at 09:45 pm

naughtyhorse, everyone –

Calm down. The notion and mechanics of geosynchronous orbits is confounding the discussion.

Look at the diagram at the start of this article. The *cable* is not in orbit. The *elevator* is not in orbit. Look at the red curving arrow. THAT is the distance a satellite would be in, to be in geosynchronous orbit (26,200 miles, or 42,164 km). The cable in the diagram is much longer than that. And the article says plainly, the cable lengths necessary are 62,000 km. So nothing in this elevator scenario is “in orbit.”

Rather, think of the cable as a string with a weight on its end. It is being spun by the earth’s rotation. Rotational inertia (or “cenrepetal” force, as some call it) causes that end-weight to want to fly away, making the cable taut. The cable is not floating like a feather– it is under a great deal of tension. It is pulling up at its anchor-point on the Earth, with presumably many tons of force. (I know: a “ton” is not a unit of force, but work with me here…)

If the cable is tugging upward with, say, 100 tons of force, then the elevator can climb it like a gymnast climbing a rope…provided the elevator weighs less than 100 tons.

Long, calming breaths, now…

cfraenkel

Posted 05 November 2006 at 12:15 am

Actually, the cable is in orbit. It’s center of mass is at geosynch. Half the mass extends down to the ground, the other half extends up. Because the whole cable is a single object, it’s all rotating at the same rate around the earth. The parts in lower orbit are moving slower than orbital velocity (that’s what makes it usefull – at the bottom you can get on with no horizontal velocity). The parts above geosynch are moving faster than ‘orbital velocity’ at that height, so that part of the cable is pulling the system up. This is the ball on a string metaphor from an earlier post, only there is no need for anything at the bottom end to hold it down. The cable is balanced with the CG at geosynch. The angular momentum of the top of the cable is equal and opposite to the force of gravity pulling on the bottom of the cable.

cfraenkel

Posted 05 November 2006 at 12:25 am

naughtyhorse: The mass of the cable is several orders of magnitude greater than the mass of the climbers. The cable designs all have counterweights at the far end of the cable to provide stability (and to make the cable length shorter) . And as each climber gets to the top, it has added to the mass of the counterweight out past the geosynch altitude, providing the additional mass that allows the next climber to climb up. Shifting a small portion of the counterweight mass inwards or farther out allows you to compensate for varying loads on the way up the cable.

Drakvil

Posted 07 January 2007 at 10:52 pm

I like the idea of the elevator, but think rockets are good things to keep, as well. If we could find a way of reducing the weight of the fuel, we’d be in business! Where’d I leave that dilithium?

Merciless

Posted 07 June 2007 at 02:49 pm

That’s all fine and dandy. Just figure it out and get one built. Actually I propose we build six of different diameters, side-by-side, like a guitars strings, get them resonating and play the non-existent aliens some freakin’ tunes. Sounds crazy HUH! Just like an elevator to outer-space is freaking absurd. Not to mention it would be the biggest of terrorist targets.

mk-ultra

Posted 23 October 2007 at 06:37 pm

Hrm.

“The problem is that the Earth’s escape velocity (the speed required to escape Earth’s gravity) is so bloody high. A rocket, which often weighs tens of thousands of pounds, must push that enormous weight up to about 420 miles per hour, and sustain such speeds for several minutes.”

420 miles per hour? If only it were that easy :-) Orbital velocities are on the order of 17,500 miles per hour. Escape velocities are closer to 25,000 miles per hour. Are you referring to the Earth’s rotational velocity (around 465 miles per *second* at the equator)?

mk-ultra

Posted 23 October 2007 at 06:56 pm

And not to belabor the point…

The weight of escape velocity capable missiles is normally measured in millions of pounds, not tens of thousands.

Just bringing this stuff up ’cause accelerating a tens-of-thousands-of-pounds vehicle to 420 mph doesn’t sound all that daunting. 747’s take 400,000 pounds to those velocities hundreds a time a day without risk of leaving orbit.

Very few craft (for example, a Saturn V) have ever accelerated six *million* pounds to over 25,000 mph :) Leaving our pale blue planet is a bit more daunting than the article hints at.

mk-ultra

Posted 23 October 2007 at 07:10 pm

Er, 1037 mph at the equator — measured on the surface.

Alchemist

Posted 26 October 2007 at 07:35 am

Total total crap. I do nanotech, and nanotubes are not going to make this work, no mater how cool they are. (Nor will the flesh eating nanobots run amok). You’ll also need anchors… MASSIVE anchors at both ends or a very rigid structure. Not … going … to … work…

Bungle

Posted 06 February 2008 at 03:18 am

(Nor will the flesh eating nanobots run amok).

meheheh… I have nothing to add on the subjects of orbits (geosynchronous or not,) or space elevators (other than the fact that it *does* sound like science fiction, or at least the kind of ‘science fact’ going around in the 50’s like there being fully colonised sections of the moon by the late 80’s etc) but I can say that Prey was a good book- despite plot holes you could drive a Mack truck through… a good book :P

Cloudshadow

Posted 04 March 2008 at 11:20 pm

Going Up….

Kd5rax

Posted 03 April 2008 at 07:36 am

JustAnotherName said: “Hi. I have an IQ of 131. Enuff sed. “

Ummmm, yeah… I know almost no one-else will read this but, uhhh… Are we supposed to be impressed or something? 131 is not even high enough for Mensa. Oooohh, I have an above average intelligence and an over-inflated ego. If all Jehova’s witnesses are that full of themselves, no wonder they get turned away. I never thought IQ was a good indicator of intelligence anyway, and that guy just keeps confirming my bias.

I personally have always loved the concept of space elevators, but have never seen any real reason to dedicate that much time and resource into it… Should’nt we be trying to improve our planet that is habitable and where life is self sustaining than send our resources into space where it all becomes unreplenishable?

Alchemist said: “Total total crap. I do nanotech, and nanotubes are not going to make this work, no mater how cool they are. (Nor will the flesh eating nanobots run amok). You’ll also need anchors… MASSIVE anchors at both ends or a very rigid structure. Not … going … to … work…”

Yea just tell people they are limited and can’t.

Great story. Remember people the details are from “wiki” and problobly wrong.
I am sure that the top of our atmosphere at sub orbit is 100 miles.

Love this site. Too bad I caught it years after the wave. Anyway…DI article.

The whole idea makes my skin crawl. I didn’t like the sensation of being on the Seattle Space Needle let alone an elevator to space.Yuck.

Just another name, I have an IQ of 143 :D 1 point from “genius” level *weep*

I feel like I’m time traveling.
NaughtyHorse from 2006 – Calm down ;)
I had the same initial reaction but I can see the math working now as i understand that the cable would have to be much further out than the GS line (geosynchronous orbit) and a weight on the end. A miscalculation could mean that our anchor tears free of the earth and flies off into space – Yes!

My new concerns are these.
1) How would you ever get enough grip on this cable to lift anything of significance up? Any accidental lubricant (ice sounds probable) and you could be in dire straights really fast.

2) By Newtons laws, every action has an equal and opposite reaction. So, if this mad scheme works, and the force being used (centrifical) would have a force acting against it…essentially slowing down the spin (our rotation). I won’t pretend to have the equations necessary so this could be a VERY insignificant amount. The moon’s pull on the tides is slowing us and the moon down anyway.

3) have you heard of the tower of babel?

DumbGuy

Posted 07 May 2009 at 05:39 am

haha, good point ValiantDefender *gets camera ready*

The problem i think is that people are using theories, calculations and all kinds of new (nano) and other types of technology to make this elevator work (i won’t bore you with my lack of extensive knowledge on therse things, i don’t know my IQ because i believe their results only show how well that person can do in IQ testing, real life is never about your Intelligence Quotient but more about the wisdom in using what intelligence you have correctly).

Laugh with me on this one, but old tricks are the best tricks, why not use a bigger/better/scientifically-enhanced/more rubbery material and construct a giant slingshot and all the space cadets can ‘shoot up’ without worrying about snow, frost, and orbital whatever-those-forces are. By now we should have had a lunar liftoff station, yes i mentioned lunar as opposed to sayng ‘a station on the moon’, shoot the cadets up in a transportable ‘projectile’ that can be caught or land without killing everybody in it, they jump into space from our lunar base, since its liftoff issues would probably cost next to nothing with our rocket/fuel system and go fix up a planet for us to live in while we carry on stuffing this one up…sorted.

thought-provoking article though…well done

SKBarry

Posted 26 July 2009 at 10:41 am

Depending on which scale you use my IQ is either 148 or 139 so I suppose that either makes me especially competent to enter into this discussion or to realize I don’t know enough to have anything to say . . . I’m going with (b). I find it fascinating to consider how we might be in a position to leave the earth for almost any purpose but I am somewhat saddened to think that we might be doing it because we have given up on our planet. I would much prefer that we try both, i.e. going other places _and_ dealing with our problems here. I’m not a big fan of small, enclosed places but I would be more than happy to take a very, very long elevator ride to get into space.

Very much enjoyed the discussion around this article, even the silly ones.

jackmagic

Posted 16 November 2009 at 03:32 am

The idea has been familiar to me for ages, and it is facinating to think of the possibilities. We would be able to harvest the asteroid fields for water and materials very easily – and it would also be the ideal way to springboard futher explorations of the solar system.

Being stuck at the bottom of a gravity well is a little restricting, and in response to the comment about looking after our planet first – im sure that job would be much easier with the cheap reasources that the solar system could offer us, and space based research would potentially offer useful new technologies! like phasers! or not, as the case may be.

Terranaut

Posted 26 May 2011 at 09:11 pm

Kd5rax said: “JustAnotherName said: “Hi. I have an IQ of 131. Enuff sed. “
Ummmm, yeah… I know almost no one-else will read this but, uhhh… Are we supposed to be impressed or something? 131 is not even high enough for Mensa. Oooohh, I have an above average intelligence and an over-inflated ego. If all Jehova’s witnesses are that full of themselves, no wonder they get turned away. I never thought IQ was a good indicator of intelligence anyway, and that guy just keeps confirming my bias.
I personally have always loved the concept of space elevators, but have never seen any real reason to dedicate that much time and resource into it… Should’nt we be trying to improve our planet that is habitable and where life is self sustaining than send our resources into space where it all becomes unreplenishable?”

kd5rax you are right! no one should have read your comment!!! are you an idiot or just a trouble maker? “just another name” was not bragging, stupid. he was trying to make the point that for the most part this was above his level of knowledge, but he wanted to be involved in the discussion anyway! I am not the brightest bulb in the pack, (only a 3.5 H.S. gpa) but we all have our strengths. i have friends who are certified geniuses, who come to me when they have a “?” in an area of knowledge i excel in.
Now for my two cents worth on this dead horse! would we not need two of these elevators? or at least a counterweight on the opposite side of the earth? it seems to my little bit of reasoning that it would through off our delicate rotational balance.

Bryan Lowder said: “I haven’t read Red Mars, but another excellent book is _Fountains_of_the_Gods_ by Arthur C. Clarke. The book is excellent in technical detail. In this book, he claims diamond tape would do the trick. Also, one failure mode is similar to the Tacoma Narrows bridge disaster– being essentially a long string, some source of energy that hit the right resonance mode would cause vibrations that would build to dangerous amplitudes. As I recall, the vibrations were actually caused by the car going up the cable. The solution was a large counterweight at the orbital end to change the resonant frequency. In the book, Mars was the first to get an elevator, because of the reduced strength requirement. Deimos became a counterweight. To avoid Phobos, the cars were timed to cause the cable to *twang* to one side at just the right moment. Not an engineering solution I would embrace.

The best discussion of this concept I have read is in Robert L. Forward’s book _Future_Magic_. Forward also discusses some really great interim concepts. One, the Launch Loop, could be executed today. Another, the Rotovator, is a stopgap solution between rockets and elevators.
In the Launch Loop, steel bars are accelerated by electromagnetic cannons and tossed into a great arc. On the other end, the bars are caught and re-accelerated. The bars interact magnetically with a pipe structure that encloses them all, and is empty of air. The loop hangs in the air without being strong enough to hold itself up. Coupling a car somehow into the stream would permit one to race to the top and fly off into orbit.
In the Rotavator, a three-spoked wheel with long cables for spokes orbits the Earth. At the same time, it is rotating as though it were “rolling” on the ground. The ends of the cables then execute a motion that essentially dives straight out of the sky. While it hangs there for a few minutes, a high-altitude airplane hooks you up to the end. Then you are jerked up into the sky. At the other end, you are flung off at twice orbital velocity– going anywhere you like. A Kevlar rotovator would be strong enough to operate on the Moon.”

Passing hobo

Posted 29 May 2016 at 10:59 am

Uhh, I don’t feel obligated to argue over the plausibility of space elevators or anything. I just feel obligated to correct one minor issue:

Escape velocity refers to the speed needed to get out of Earth’s gravity well, not the speed needed to achieve orbit. Orbit isn’t about getting so high up you’re weightless. It’s basically about moving so fast gravity can’t pull in a consistent direction.

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